a single phone call opening a world of possibility. Today president obama surprised everyone, announcing he had a personal phone conversation with the new president of iran, the first direct contact between leaders since 1979. So the question tonight, is this the best chance for a breakthrough in the middle east in 30 years? Will the new leader of iran really deliver? Abc's chief white house correspondent jonathan karl on the latest developments from the white house. John. Reporter: History was made today, diane with that 15 minute phone call. A potential opening to a country the u.S. Has accused of trying to build nuclear weapons and supporting terrorism. The storming of the u.S. Embassy in tehran and the 440 day hostage crisis that followed has a u.S. President spoken to an iranian president. The very fact this was the first communications between an american and iranian president since 1979 underscores the deepness between our countries and indicates the prospect of moving beyond that difficult history. Reporter: News of the call broke with a tweet from iran's president shortly before president obama announced it, rouhani turned down a face to face meeting when both men were in new york on tuesday, but the call was his idea. Rouhani has been in new york all week, speaking at the u.N. And vowing warmer relations with the united states. The obstacles are huge, for years war with iran has seemed more likely than diplomatic progress. The president says he sees a chance for a big change. Beginning with renewed talks on iran'suclear program. I believeve we have a responsibility to pursue diplomacy, and a unique opportunity to make progress with the new leadership in tehran. Reporter: Right after the president touted his historic conversation with the president of iran, he lashed out at a group he hasn't been talking to, republicans in congress, who he blamed for putting the government on a path to shutdown in just three days. Nobody gets to threaten the full faith and credit of the united states just to extract political concessions. No one gets to hurt our economy and millions of innocent people just because there are a couple laws you do not like. Reporter: History was made with the obama rouhani phone conversation, there has been no phone calls this week between the president and the speaker of the house. Diane, it is no exaggeration to say that the president has made more progress this week with iran than he has with republicans in congress. All right. Give us the real story. Is there going to be a shutdown next week? And how long? Reporter: I think there quite likely will be, I put the odds at 50-50 this morning now there is more likely than not there will be a shutdown next week for a couple days. The much bigger problem when the country faces the ris of default, if congress doesn't raise the amount the government can borrow. All right, jonathan karl at the white house tonight. Thank you. And on sunday, george stephanopoulos will have an exclusive interview with iran's foreign minister live, and that is sunday on this week.

This transcript has been automatically generated and may not be 100% accurate.